/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.servlet.jsp.tagext;

/**
 * Optional class provided by the tag library author to describe additional
 * translation-time information not described in the TLD. The TagExtraInfo class
 * is mentioned in the Tag Library Descriptor file (TLD).
 * 
 * <p>
 * This class can be used:
 * <ul>
 * <li>to indicate that the tag defines scripting variables
 * <li>to perform translation-time validation of the tag attributes.
 * </ul>
 * 
 * <p>
 * It is the responsibility of the JSP translator that the initial value to be
 * returned by calls to getTagInfo() corresponds to a TagInfo object for the tag
 * being translated. If an explicit call to setTagInfo() is done, then the
 * object passed will be returned in subsequent calls to getTagInfo().
 * 
 * <p>
 * The only way to affect the value returned by getTagInfo() is through a
 * setTagInfo() call, and thus, TagExtraInfo.setTagInfo() is to be called by the
 * JSP translator, with a TagInfo object that corresponds to the tag being
 * translated. The call should happen before any invocation on validate() and
 * before any invocation on getVariableInfo().
 * 
 * <p>
 * <tt>NOTE:</tt> It is a (translation time) error for a tag definition in a TLD
 * with one or more variable subelements to have an associated TagExtraInfo
 * implementation that returns a VariableInfo array with one or more elements
 * from a call to getVariableInfo().
 */

public abstract class TagExtraInfo {

	/**
	 * Sole constructor. (For invocation by subclass constructors, typically
	 * implicit.)
	 */
	public TagExtraInfo() {
	}

	/**
	 * information on scripting variables defined by the tag associated with
	 * this TagExtraInfo instance. Request-time attributes are indicated as such
	 * in the TagData parameter.
	 * 
	 * @param data
	 *            The TagData instance.
	 * @return An array of VariableInfo data, or null or a zero length array if
	 *         no scripting variables are to be defined.
	 */
	public VariableInfo[] getVariableInfo(TagData data) {
		return ZERO_VARIABLE_INFO;
	}

	/**
	 * Translation-time validation of the attributes. Request-time attributes
	 * are indicated as such in the TagData parameter. Note that the preferred
	 * way to do validation is with the validate() method, since it can return
	 * more detailed information.
	 * 
	 * @param data
	 *            The TagData instance.
	 * @return Whether this tag instance is valid.
	 * @see TagExtraInfo#validate
	 */

	public boolean isValid(TagData data) {
		return true;
	}

	/**
	 * Translation-time validation of the attributes. Request-time attributes
	 * are indicated as such in the TagData parameter. Because of the higher
	 * quality validation messages possible, this is the preferred way to do
	 * validation (although isValid() still works).
	 * 
	 * <p>
	 * JSP 2.0 and higher containers call validate() instead of isValid(). The
	 * default implementation of this method is to call isValid(). If isValid()
	 * returns false, a generic ValidationMessage[] is returned indicating
	 * isValid() returned false.
	 * </p>
	 * 
	 * @param data
	 *            The TagData instance.
	 * @return A null object, or zero length array if no errors, an array of
	 *         ValidationMessages otherwise.
	 * @since 2.0
	 */
	public ValidationMessage[] validate(TagData data) {
		ValidationMessage[] result = null;

		if (!isValid(data)) {
			result = new ValidationMessage[] { new ValidationMessage(data
					.getId(), "isValid() == false") };
		}

		return result;
	}

	/**
	 * Set the TagInfo for this class.
	 * 
	 * @param tagInfo
	 *            The TagInfo this instance is extending
	 */
	public final void setTagInfo(TagInfo tagInfo) {
		this.tagInfo = tagInfo;
	}

	/**
	 * Get the TagInfo for this class.
	 * 
	 * @return the taginfo instance this instance is extending
	 */
	public final TagInfo getTagInfo() {
		return tagInfo;
	}

	// private data
	private TagInfo tagInfo;

	// zero length VariableInfo array
	private static final VariableInfo[] ZERO_VARIABLE_INFO = {};
}
